Radio communication networks were originally developed primarily to provide voice services over circuit-switched networks. The introduction of packet-switched bearers in, for example, the so-called 2.5G and 3G networks enabled network operators to provide data services as well as voice services. Eventually, network architectures will likely evolve toward all Internet Protocol (IP) networks which provide both voice and data services. However, network operators have a substantial investment in existing infrastructures and would, therefore, typically prefer to migrate gradually to all IP network architectures in order to allow them to extract sufficient value from their investment in existing infrastructures. Also to provide the capabilities needed to support next generation radio communication applications, while at the same time using legacy infrastructure, network operators could deploy hybrid networks wherein a next generation radio communication system is overlaid onto an existing circuit-switched or packet-switched network as a first step in the transition to an all IP-based network. Alternatively, a radio communication system can evolve from one generation to the next while still providing backward compatibility for legacy equipment.
One example of such an evolved network is based upon the Universal Mobile Telephone System (UMTS) which is an existing third generation (3G) radio communication system that is evolving into High Speed Packet Access (HSPA) technology. Yet another alternative is the introduction of a new air interface technology within the UMTS framework, e.g., the so-called Long Term Evolution (LTE) technology. Target performance goals for LTE systems include, for example, support for 200 active calls per 5 MHz cell and sub 5 ms latency for small IP packets. Each new generation, or partial generation, of mobile communication systems add complexity and abilities to mobile communication systems and this can be expected to continue with either enhancements to proposed systems or completely new systems in the future. The 3rd Generation Partnership Project (3GPP) is a standards-developing organization that is continuing its work of evolving HSPA and LTE, and creating new standards that allow for even higher data rates and improved functionality.
In a radio access network implementing LTE, a user equipment (UE), alternatively also referred to herein as a mobile terminal or a user terminal, is wirelessly connected to a base station. The term “base station” is used herein as a generic term. In the LTE architecture an evolved NodeB (eNodeB or eNB) may correspond to the base station, i.e., a base station is a possible implementation of the eNodeB. However, the term “eNodeB” is also broader in some senses than the conventional base station since the eNodeB refers, in general, to a logical node. The term “base station” is used herein as inclusive of a base station, a NodeB, an eNodeB or other nodes specific for other architectures. An eNodeB in an LTE system handles transmission and reception in one or several cells. In LTE several different types of physical downlink (DL) channels and physical uplink (UL) channels have been specified. Physical Uplink Shared Channel (PUSCH) is a physical uplink channel that is used by the UE for data transmission after the UE has been assigned an uplink resource for data transmission on the PUSCH. The PUSCH also carries control information. Physical Uplink Control Channel (PUCCH) is a physical uplink channel which carries control information in the form of downlink acknowledgements and Channel Quality Indicator (CQI) related reports.
Uplink power control is used both on the PUSCH and on PUCCH. The idea behind uplink power control is to ensure that the mobile terminal transmits with sufficient power, but at the same time not be too high, since that would only increase the interference to other users in the network. In both cases, a parameterized open loop combined with a closed loop mechanism is used. Roughly, the open loop part is used to set a point of operation, around which the closed loop component operates. Different parameters, targets and ‘partial compensation factors’, for user and control plane are used.
In more detail, for PUSCH the mobile terminal sets the output power according to
                    P                  PUSCH          ,          c                    ⁡              (        i        )              =          min      ⁢                        {                                                                                                                P                                              CMAX                        ,                        c                                                              ⁡                                          (                      i                      )                                                        ,                                                                                                                          10                    ⁢                                                                                  ⁢                                                                  log                        10                                            ⁡                                              (                                                                              M                                                          PUSCH                              ,                              c                                                                                ⁡                                                      (                            i                            )                                                                          )                                                                              +                                                            P                                                                        O                          ⁢                          _                          ⁢                          PUSCH                                                ,                        c                                                              ⁡                                          (                      j                      )                                                        +                                                                                    α                        c                                            ⁡                                              (                        j                        )                                                              ·                                          PL                      c                                                        +                                                            Δ                                              TF                        ,                        c                                                              ⁡                                          (                      i                      )                                                        +                                                            f                      c                                        ⁡                                          (                      i                      )                                                                                                    }                ⁢                                  [        dBm        ]              ,where PCMAX,c is the maximum transmit power for the mobile terminal for the serving cell c, MPUSCH,c is the number of resource blocks assigned for the serving cell c, PO—PUSCH,c and αc control the target received power for the serving cell c, PLc is the estimated pathloss for the serving cell c, ΔTF,c is transport format compensator for the serving cell c and ƒc is a UE specific offset or ‘closed loop correction’ for the serving cell c. The function ƒmay represent either absolute or accumulative offsets depending on the operating mode of the closed loop power control. For a more detailed description of the uplink power control for PUSCH see section 5.1.1.1 of the standards document 3GPP TS. 36.213 v.10.2.0. A similar uplink power control has been specified for the PUCCH in section 5.1.2.1 of the same standards document.
The closed loop power control can be operated in two different modes either an accumulated or an absolute mode. Both modes are based on transmit power control (TPC) commands which are part of the downlink control signaling. When absolute power control is used, the closed loop correction function is reset every time a new TPC command is received. When accumulated power control is used, the TPC command is a delta correction with regard to the previously accumulated closed loop correction.
Of particular interest for this disclosure is a problem related to accumulated power control. The base station can filter the mobile terminal's power in both time and frequency to provide an accurate power control operating point for the mobile terminal. The accumulated power control command is defined as ƒc(i)=ƒc(i−1)+δPUSCH,c(i−KPUSCH), where δPUSCH,c is the TPC command received in KPUSCH subframe before the current subframe i and ƒc(i−1) is the accumulated power control value. If the UE has reached PCMAX,c for serving cell c, positive TPC commands, i.e. commands indicating a raise in transmit power, for serving cell c shall not be accumulated. If the UE has reached a defined minimum power, negative TPC commands, i.e. commands indicating a decrease in transmit power, shall not be accumulated.
There are different occasions when the accumulated power control value is reset, such as                at cell-change,        when entering/leaving Radio Resource Control (RRC) active state,        when an absolute TPC command is received,        when PO—UE—PUCCH is received, which implies reconfiguration by a higher layer, and        when the mobile terminal (re)synchronizes.        
In the case of reset, the accumulated power control value is reset to ƒ(0)=ΔPrampup+δmsg2, where δmsg2 is the TPC command indicated in random access response and ΔPrampup corresponds to the total power ramp-up from a first to a last preamble.
The PUCCH power control has in principle the same configurable parameters as described above for PUSCH, with the exception that PUCCH only has full pathloss compensation, i.e. does only cover the case of α=1.
The power control for Sounding Reference Signal (SRS) follows the power control for PUSCH with the addition of some SRS specific offsets.
There are two different ways for the UE to receive TPC commands on the PUSCH. The UE always receives a TPC command when it receives a Downlink Control Information (DCI) format for an UL PUSCH transmission. In Rel-10 of the 3GPP LTE standard, this corresponds to DCI format 0/4. The UE can also receive TPC commands by DCI format 3/3A. DCI format 3/3A are DCI messages that are dedicated to be used for TPC commands. The UE is assigned a specific radio network temporary identity (RNTI) that the UE uses to identify whether the received DCI format 3/3A is actually sent to it. Further it is possible to assign the UE with one RNTI for PUCCH and one for PUSCH TPC commands. DCI format 3/3A contains a long bit vector. Several UEs receive the same DCI format 3/3A message, this by assigning them with the same RNTI. Each UE identifies its TPC command within the received DCI format 3/3A with a code point that it is assigned to. The TPC command consists of 1 bit if DCI format 3A is received and 2 bits if DCI format 3 is received for each UE.
However, there are some problems associated with determining when to accumulate TPC commands in radio communication systems, such as those systems described above. These need to be overcome and are described in more detail below.